I think you’re right that you need something at the back. It would look quite odd if a sash came forward from the side seams but the back was bare. Somehow it works the opposite way 😉
If you use a cotton and have a full sash it will be heavy and I’d worry it will sag at the front – unless you tie it quite tight!
You certainly could put the back sash pieces on the front, then have short pieces on each side at the back, but then all that chopping up of the sash at side and back seams may look really weird.
Not helping yet, right?…. 🙂
Would your daughter consider this compromise: the view A narrow belt, with a bunch of Dior Roses (there’s a tutorial on the blog) and a couple of mini bows. Almost like a corsage on the belt.
You could even make a matching headband with Dior Roses on it.